1. Field of the Invention
The present invention relates to a touch panel.
2. Description of the Related Art
A touch panel is an input device usually provided in front of a display and capable of inputting data. A user can directly input data based on information visually grasped by viewing the display through the touch panel, so that the touch panel is used in various ways.
A resistive touch panel is widely known. For the resistive touch panel, transparent conductive layers are respectively formed on an upper conductive substrate and on a lower conductive substrate where the transparent conductive layers are positioned to face each other. When force is applied to a point of the upper conductive substrate, the transparent conductive layers of the upper conductive substrate and the lower conductive substrate contact at that point. At this time, a potential gradient is generated on one of the transparent conductive layers so that a coordinate position of the pushed point can be detected by reading an electric potential of the other of the transparent conductive layers.
Resistive touch panels mainly include a four-wire type and a five-wire type. For the four-wire type, electrodes for applying potential gradients in an X-axis direction and in a Y-axis direction are respectively provided on one and the other of the upper conductive substrate and the lower conductive substrate. For the five-wire type, electrodes for applying potential gradients in both the X-axis direction and the Y-axis are provided on the lower conductive substrate, and the upper conductive substrate functions as a probe to read an electric potential (see Patent Documents 1, 2 and 3).
Specifically, with reference to FIG. 1 and FIG. 2, the four-wire type touch panel is explained. FIG. 1 is a cross-sectional view of a four-wire type touch panel. FIG. 2 is a perspective view of the four-wire type touch panel.
The four-wire type touch panel includes an upper electrode substrate including a film 10 and a transparent conductive layer 30 which is formed at one surface of the film 10, a lower electrode substrate including a glass 20 and a transparent conductive layer 40 which is formed at one surface of the glass 20, and a spacer 50. The spacer 50 is provided between the transparent conductive layer 30 and the transparent conductive layer 40 such that the transparent conductive layer 30 and the transparent conductive layer 40 facing each other. The four-wire type touch panel is electrically connected to a host computer or the like through a cable, not shown in the drawings.
Electrodes 31 and 32 are provided on the surface of the film 10, on which the transparent conductive layer 30 is also formed, at both ends in an X-axis direction along a Y-axis direction. Similarly, electrodes 41 and 42 are provided on the surface of the glass 20, on which the transparent conductive layer 40 is also formed, at both ends in the Y-axis direction along the X-axis direction.
For the four-wire type touch panel, an operation of detecting a position of the touch panel while being touched is explained.
First, as shown in FIG. 3, voltages are applied to the electrodes 31 and 32 of the upper electrode substrate. Specifically, the electrode 31 is grounded (0V) and the electrode 32 is applied with Vcc, for example, 5V. At this state, when a touch pen 60 or the like touches a point “A” of the touch panel, the transparent conductive layer 30 of the upper electrode substrate and the transparent conductive layer 40 of the lower electrode substrate contact at the point “A”. As a potential gradient is generated in the X-axis direction, the electric potential at the point “A” can be detected by measuring the electric potential of the transparent conductive layer 40 when the transparent conductive layer 30 and the transparent conductive layer 40 are contacted at the point “A”. The electric potential corresponds to a value of the voltage applied by the electrodes 32 and 31 and divided by the resistance of the transparent conductive layer 30 at the point “A” in the X-axis direction. The electric potential is detected by a voltage meter 70 through the electrode 41 provided on the transparent conductive layer 40. Subsequently, as shown in FIG. 4, an X coordinate of the point “A” is detected based on the voltage “Va” measured by the voltage meter 70.
Next, as shown in FIG. 5, voltages are applied to the electrodes 41 and 42 of the lower electrode substrate. Specifically, the electrode 41 is grounded (0V) and the electrode 42 is applied with Vcc, for example, 5V. Similar to the above described upper electrode substrate, when the touch pen 60 or the like touches the point “A” of the touch panel, the transparent conductive layer 30 of the upper electrode substrate and the transparent conductive layer 40 of the lower electrode substrate contact at the point “A”. As the transparent conductive layer 40 is applied with voltages by the electrodes 41 and 42 to generate a potential gradient in the Y-axis direction and the transparent conductive layer 30 and the transparent conductive layer 40 are contacted at the point “A”, the electric potential at the point “A” can be detected by measuring the electric potential of the transparent conductive layer. The electric potential corresponds to a value of the voltage applied by the electrodes 41 and 42 and divided by the resistance of the transparent conductive layer 40 at the point “A” in the Y-axis direction. The electric potential is detected by a voltage meter 80 through the electrode 31 provided on the transparent conductive layer 30. Subsequently, as shown in FIG. 6, a Y coordinate of the point “A” is detected based on the voltage “Vb” measured by the voltage meter 80.
With the above operations, the X coordinate and the Y coordinate of the point “A” can be obtained so that two-dimensional positions of the point “A” can be grasped.
For the four-wire type touch panel, the operation in which the transparent conductive layer 30 of the upper electrode substrate is applied with voltages and the transparent conductive layer 40 of the lower electrode substrate detects the electric potential, and the operation in which the transparent conductive layer 40 of the lower electrode substrate is applied with voltages and the transparent conductive layer 30 of the upper electrode substrate detects the electric potential, are alternately performed to enable a successive positional detection.
However, for the above described four-wire type touch panel, it is capable of detecting a position when a single point is touched, but it is impossible to detect plural positions when plural points are touched at the same time.
As shown in FIG. 7, similar to that shown in FIG. 3, the electrodes 31 and 32 of the upper electrode substrate are applied with voltages, for example, the electrode 31 is grounded (0V) and the electrode 32 is applied with Vcc, 5V. At this state, if touch pens 61 and 62 or the like touch the touch panel at points “B” and “C”, respectively, at the same time, the coordinates of the points “B” and “C” cannot be detected.
When the two points “B” and “C” of the touch panel are touched at the same time, the electric potential Vx at a middle point of the points “B” and “C” is detected at the transparent conductive layer 40, as shown in FIG. 8. Therefore, even if two points are touched on the touch panel, as the detected electric potential is just a single value, it is detected as if a single point is touched. Thus, each of the two coordinates corresponding to the points “B” and “C” cannot be detected.
Therefore, in Patent Document 4, a touch panel capable of detecting multi-touches by electrically connecting resistors to the transparent conductive layers 30 and 40, respectively.